From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7E5ACC282C3 for ; Tue, 22 Jan 2019 14:57:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 467BA20870 for ; Tue, 22 Jan 2019 14:57:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="uxnurEWp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728971AbfAVO5v (ORCPT ); Tue, 22 Jan 2019 09:57:51 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:44314 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728795AbfAVO5v (ORCPT ); Tue, 22 Jan 2019 09:57:51 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=ubc/EeKgBxh6zaeMi0e7CVRJR36Rk40o1knBVNzRVgo=; b=uxnurEWpOwxfX07blsFss6LMX QIsijql4IW5MQwVhqLc1fUPwBWjpaJrIvR4EoZxJIcHicV4VIjfWgyXF7KOYNGh04kLpi5OjW7KgK j5cMe9L/dy1u8nafjWzsgStT8f7mH2EpJyUZmeUzFz3cHn5oPOFqjLPcp3QB7j1vorE44z68x+FrG II+yp3j2g+106iMVvUW/AfSX2juhT1G5JeCZbZsU7rGO0td0suZVWaKtMteAmI+oKL8uZh+UMKskw +Hl/hdwcuFfSUUjEMIfyUmg31A1R50ZOnghv3X5fI8N5oMmqUXRoKS+LeWuhFImUI8RRbSoyGGGu1 EQ3SM2kAw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1glxUn-0000N4-Bf; Tue, 22 Jan 2019 14:57:45 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id D1C0020EF9B32; Tue, 22 Jan 2019 15:57:42 +0100 (CET) Date: Tue, 22 Jan 2019 15:57:42 +0100 From: Peter Zijlstra To: Patrick Bellasi Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, linux-api@vger.kernel.org, Ingo Molnar , Tejun Heo , "Rafael J . Wysocki" , Vincent Guittot , Viresh Kumar , Paul Turner , Quentin Perret , Dietmar Eggemann , Morten Rasmussen , Juri Lelli , Todd Kjos , Joel Fernandes , Steve Muckle , Suren Baghdasaryan Subject: Re: [PATCH v6 05/16] sched/core: uclamp: Update CPU's refcount on clamp changes Message-ID: <20190122145742.GQ27931@hirez.programming.kicks-ass.net> References: <20190115101513.2822-1-patrick.bellasi@arm.com> <20190115101513.2822-6-patrick.bellasi@arm.com> <20190121153308.GL27931@hirez.programming.kicks-ass.net> <20190121154412.fak2t2iquj3aixtu@e110439-lin> <20190122093704.GM27931@hirez.programming.kicks-ass.net> <20190122104305.6vjx37muqsxm536t@e110439-lin> <20190122132817.GG13777@hirez.programming.kicks-ass.net> <20190122140115.twtx646vewm757ca@e110439-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190122140115.twtx646vewm757ca@e110439-lin> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 22, 2019 at 02:01:15PM +0000, Patrick Bellasi wrote: > On 22-Jan 14:28, Peter Zijlstra wrote: > > On Tue, Jan 22, 2019 at 10:43:05AM +0000, Patrick Bellasi wrote: > > > On 22-Jan 10:37, Peter Zijlstra wrote: > > > > > > Sure, I get that. What I don't get is why you're adding that (2) here. > > > > Like said, __sched_setscheduler() already does a dequeue/enqueue under > > > > rq->lock, which should already take care of that. > > > > > > Oh, ok... got it what you mean now. > > > > > > With: > > > > > > [PATCH v6 01/16] sched/core: Allow sched_setattr() to use the current policy > > > <20190115101513.2822-2-patrick.bellasi@arm.com> > > > > > > we can call __sched_setscheduler() with: > > > > > > attr->sched_flags & SCHED_FLAG_KEEP_POLICY > > > > > > whenever we want just to change the clamp values of a task without > > > changing its class. Thus, we can end up returning from > > > __sched_setscheduler() without doing an actual dequeue/enqueue. > > > > I don't see that happening.. when KEEP_POLICY we set attr.sched_policy = > > SETPARAM_POLICY. That is then checked again in __setscheduler_param(), > > which is in the middle of that dequeue/enqueue. > > Yes, I think I've forgot a check before we actually dequeue the task. > > The current code does: > > ---8<--- > SYSCALL_DEFINE3(sched_setattr) > > // A) request to keep the same policy > if (attr.sched_flags & SCHED_FLAG_KEEP_POLICY) > attr.sched_policy = SETPARAM_POLICY; > > sched_setattr() > // B) actually enforce the same policy > if (policy < 0) > policy = oldpolicy = p->policy; > > // C) tune the clamp values > if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) > retval = __setscheduler_uclamp(p, attr); > > // D) tune attributes if policy is the same > if (unlikely(policy == p->policy)) > if (fair_policy(policy) && attr->sched_nice != task_nice(p)) > goto change; > if (rt_policy(policy) && attr->sched_priority != p->rt_priority) > goto change; > if (dl_policy(policy) && dl_param_changed(p, attr)) > goto change; if (util_changed) goto change; ? > return 0; > change: > > // E) dequeue/enqueue task > ---8<--- > > So, probably in D) I've missed a check on SCHED_FLAG_KEEP_POLICY to > enforce a return in that case... > > > Also, and this might be 'broken', SETPARAM_POLICY _does_ reset all the > > other attributes, it only preserves policy, but it will (re)set nice > > level for example (see that same function). > > Mmm... right... my bad! :/ > > > So maybe we want to introduce another (few?) FLAG_KEEP flag(s) that > > preserve the other bits; I'm thinking at least KEEP_PARAM and KEEP_UTIL > > or something. > > Yes, I would say we have two options: > > 1) SCHED_FLAG_KEEP_POLICY enforces all the scheduling class specific > attributes, but cross class attributes (e.g. uclamp) > > 2) add SCHED_KEEP_NICE, SCHED_KEEP_PRIO, and SCED_KEEP_PARAMS > and use them in the if conditions in D) So the current KEEP_POLICY basically provides sched_setparam(), and given we have that as a syscall, that is supposedly a useful functionality. Also, NICE/PRIO/DL* is all the same thing and depends on the policy, KEEP_PARAM should cover the lot And I suppose the UTIL_CLAMP is !KEEP_UTIL; we could go either way around with that flag. > In both cases the goal should be to return from code block D). I don't think so; we really do want to 'goto change' for util changes too I think. Why duplicate part of that logic?